Piston-ring groove



March s, 1927. 1,619,993

H. STOLL PISTON RING GROOVE Filed Aug. 3l, 1925 atlfoz nu! Patented Mar. 8, 1927.

,UNITED STAT-Es:

HERMAN STOLL, OF DETROIT, MICHIGAN, ASSIGNOR TO GENERAL 'MOTORS CORPORA- r TION, OF DETROIT, MICHIGAN, A CORPORATION OF DELAWARE. i

IPISTON-RING GROOVE.

Application filed August 31, 1925. Serial No. 53,601.

This invention has to do with pistons, such as are used in internal combustion engines, which are customarily provided with grooves in which the usual piston rings are seated. These grooves are formed in the piston by applying thereto a cutting tool having a fiat cutting edge. After some use the cutting edge becomes Worn at the corners, resulting in the production of a groove the bottom of which is slightly concave. When the piston ring which {cus-4 tomarily has a fiat rear wall, is now seated in the groove, it engages at the high points,

that is, at the sides ot the groove only, and,`

as a result, projects further beyond the surtace of the piston' than is desired.

To avoid this inaccuracy I have preferred to form umy groove with a bottom which is slightly higher at the center than at the sides. While this may be accomplished by using a tool having a cutting edge of various configurations, I have. preferred to use 'one the cutting edge 'p of which is concave. lVith this construction the corners of the tool may wear to a considerable degree and yet produce a groove the bottom of which is higher at the center than at the sides. The

reduction in depth of the groove at thesides,

incident to .wearingx of the tool, will not aff fect the extent of projection of the rings beyond the sides of the piston.

In the drawings Figure 1 is a side elevation of a piston of conventional type, the piston rings'beingshown in section;

Figure 2 is an enlarged view ot' a `portion ot the construction shown in Figure ,1. Reference character 2 indicates a. piston of conventional type. The ring grooves are -indicated .by reference character 41E-and the rlngs by the reference character 6. The rings are'illustrated as rectangular in cross section', but 'this is lnot essential and' any `other type of ring may be substituted for that shown.

My invention resides in so forming the surfaces constituting the backs of the rings grooves. of Ways. l have chosen to illustrate theand the bottoms of the grooves that they will Contact only at the centers of, the.

This 'may be done in a number bottoms of the grooves as of convexcontour as shownat l0, so that the Contact between the back ot thering and the bottom ot' thcl groove will be substantially along a line extending around the piston and midway fot the width of the groove. It is obvious that it is not essential that the bottom of the groove be convex so long asthe central portion of the bottom of the groove be higher than the side portions. l

As previously pointed out, with this construction the extent ot projection of the piston rings from the sides ot' the pistons l is maintained constant despite lack ot' exact.

uniformity inmaking the cut at the sides ot' the grooves.v

What I claiin and desire to protect'by Letters Patentis: v i

1.. A combination of a piston having 0a groove therein having parallel sides to permit readyl removal of the cutting tool, a ring in the groove, the bottom of the ring and the bottom of the groove being sotormed as to Contact onlyl at substantially the center of the groove, there being clearance lbetween the back of the ring and the bottomv of the groove at the sides of the latter.

2. A combination of a piston having a groove therein having parallel sides to perm1t ready removal of the cutting tool` the bottom of the groove'being convex and thel ring having a rear wall adapted to engage the bottom' ofthe groove at the center only.

3. A combination of a piston having a groove therein having parallel sides to per-v mit ready removal otthe cutting tool, thc

bottom of the groove .being convex and.' a` ring having a latrear Wall adapted to en` gage the bottom of the groove.

In testimony whereoic I aiiix my signature.

HERMAN sfroLL. 

